Suspended-body flow meters have been used since the middle of the past century to find volume and mass flow in closed pipelines. Today they can still be found in roughly one out of every five flow-meter devices in the chemical and processing industries.
A suspended-body flow meter, in its simplest embodiment, consists of a conical measuring tube and the suspended body. The measuring tube is a conical tube that is wider at the top and through which the liquid or gas stream to be measured flows from bottom to top, in which the suspended body, a measuring body that can move freely vertically and is designed for the purpose, is found, which forms a throttle site along with the measuring tube. The density of the suspended body is greater than that of the fluid. Depending on the flow, the suspended body is set in the built-up state at a certain height in the measuring tube which is caused by the equilibrium of the hydrodynamic force caused by the flow transmitted to the suspended body and the difference in the weight and lift forces of the suspended body. This height is either read directly by the observer on a scale on a glass measuring tube or is transmitted through a magnetic coupling to an external scale and/or an electrical transducer. The suspended-body flow meters in question have one like this, in which the height of the suspended body can be transmitted by a magnetic coupling via an external follower magnet to a scale and/or an electrical transducer.
Besides the forms of embodiment with conical measuring tubes and ball-shaped or sharp-edged suspended bodies, measuring tubes with a measuring orifice and a conical suspended body within the orifice opening can also be used. It is also conceivable to arrange the measuring tube not vertically, and in this case it is necessary to replace the weight force of the suspended body. However, the invention is independent of the potential variations described in the design of a suspended-body flow meter.
A suspended body flow meter is known from the prior art (see U.S. Pat. No. 4,944,190), which has at least one follower magnet arranged outside the measuring tube that follows the movements of the permanent magnets here directly forming the suspended body, where the follower magnet in the state of the art is constructed to be annular and this annular follower magnet is diametrically magnetized, hence staggered by 180.degree. and has one north and one south pole.
The problem in the prior art is that the annular follower magnet has different angles of rotation depending on the nominal width of the measuring tube, the stroke of the suspended body remaining equal. This means that when suspended-body flow meters are produced, dependent on the nominal width of the measuring tube used, either scales with a different spread are used to display the movements of the follower magnet or other means of correction must be used. Such means of correction, which permit the use of scales with the same spread, consist of using counterweights or auxiliary rods, for example.
The problem outlined above can basically be avoided by detecting the movements of the follower magnet electronically with magnetic field sensors and then correcting the different angle of rotation using an amplification factor dependent on the nominal width. But in many cases, this is not wanted, since one decisive advantage of the suspended-body flow meters is often that, for example, in contrast to a magnetically inductive flow meter, it also supplies a measured value without auxiliary energy. For this reason, many suspended-body flow meters have an electronic measurement signal output, but at the same time dispense with the purely mechanical display.